In machines for preparing coffee or the like it is known to froth, whip a liquid by using a jet of steam which is conveyed by means of a tube and flows out from a nozzle, to be used for preparing hot beverages such as for example the so-called “cappuccino”.
Such steam jet is propelled under the free surface of the beverage to be frothed and, in order to obtain correct whipping, the operator must have high manual skills in order to obtain repeatable and quality results.
For this reason, accessories known in the jargon as “cappuccinatori” (frothers) have been devised which are designed to be coupled to a steam delivery tube, which make the whipping easier by providing inside them an organized fluid dynamics, in order to make the result independent of the user's skill. Sometimes such accessories known in the jargon as frothers, are incorrectly termed “emulsifiers”, although this term does not rigorously reflect the action performed by the accessory on the beverage to be frothed.
As is known, the emulsion of a liquid entails the mixing of at least two fluids in liquid phase that are not miscible. In this particular case, the mixing of fluids in the gaseous phase (steam and air) with a fluid in the liquid phase (milk) forms froth. More precisely, the turbulence, which is generated thanks to the speed of the steam flow, makes the liquid incorporate air and, together with the heating induced by the steam, the frothing and mixing of the beverage is achieved.
In particular, it is known to use devices which, by way of a plurality of passage channels which are parallel to the steam jet, allow to aspirate air and the liquid to be whipped by making them converge in a mixing region, in which the steam jet converges as well. The channels can be separated from each other, so that each one conveys a respective flow (air, liquid or steam) in a single mixing point at the steam nozzle.
This process is allowed by the Venturi effect that is created within the device. More precisely, the steam jet travels through a main duct at high speed in order to create a partial vacuum in the ducts for aspirating the air and the liquid to be frothed, which are connected to the main duct.
In this manner, the air and the liquid to be frothed are both aspirated and conveyed into the main duct, in which the mixing of the three fluids takes place, with the consequent whipping and mixing of the beverage.
A drawback of the background art is that it is not always possible to obtain optimum froths, due to the inexperience of the user or to the ineffective mixing of air, liquid and steam.
Another drawback of frothing devices of the known type resides in that they are not easy to clean, especially inside cavities and blind spots. The need to perform cleaning operations on these types of components, especially those installed on espresso coffee machines, is in fact frequent, because during use the heating and the particular type of liquid to be whipped, i.e., milk, causes the adhesion of residues which over time become increasingly harder to remove.
Moreover, known frothing devices have a large number of components, which cause the disassembly operations that precede cleaning to be laborious.